1. Field of the Invention
The present invention relates to a method for displaying a drive state of a backlight in a liquid crystal display device, and more particularly, to an apparatus and method for displaying a drive state of a backlight in a liquid crystal display device which checks a drive state of a backlight lamp and notifies the checked result to an outside entity.
2. Description of the Related Art
With the rapid development in the field of information and technology, the importance of a flat panel display device for displaying a variety of information has recently increased. As a representative example of the flat panel display device, a liquid crystal display (LCD) device is an apparatus which displays an image using an optical anisotropy of a liquid crystal, and has many advantages including being small in size, thin in thickness, low in power consumption, high definition, and the like.
Since the liquid crystal display device does not have a self light-emitting characteristic, a backlight unit supplying light is required to implement an image. The backlight unit uses a Cold Cathode Fluorescent Lamp (CCFL) or an External Electrode Fluorescent Lamp (EEFL) as a light source. Light emitted from the CCFL or EEFL is transmitted through a light guide plate to be reflected onto a liquid crystal display screen directly below the liquid crystal display device.
The Cold Cathode Fluorescent Lamp (CCFL) and the External Electrode Fluorescent Lamp (EEFL) have similar characteristics to each other. Here, the EEFL does not have an electrode or a filament within a glass tube, instead, covers each outer wall of both ends of a lamp with a carbon or silver powder so as to use it as an electrode. For the EEFL, a condenser is provided in each lamp, thereby enabling distribution of a current when connecting the lamps in parallel. Thus, it has an advantage of using a plurality of lamps by connecting them in parallel to one inverter. The tube skin temperature in the EEFL is lower than that in the CCFL, which greatly reduces degradation of a frame or color change of a screen when an advertising signboard is manufactured.
However, the CCFL uses a relatively great amount of mercury which is environmentally regulated, and is connected to the inverter through a power line, thereby causing a leakage of a current. In addition, the CCFL has only 10,000˜50,000 hours of lifetime, thereby being undesirable for use in a television. From the aspect of reliability, the CCFL is vulnerable to vibration or an impact, and from the aspect of color reproduction, visibility thereof is highly reduced when compared to a conventional a cathode ray tube (CRT).
Due to such reasons, a white LED or a color LED, which overcomes the demerits of the CCFL, has drawn much attention as a light emitting diode having high reliability, with advantages of high color reproduction, environmental-friendly characteristics, and long lifetime.
FIG. 1 is a block diagram of a backlight driving device of a related art liquid crystal display device. As shown in the drawing, the backlight driving device may include an inverter 11 for converting a DC voltage inputted from an external source into a boosted AC voltage and outputting the same to a backlight lamp (CCFL/EEFL) 12; the backlight lamp 12 lighted by the boosted AC voltage outputted from the inverter 11 and supplying a backlight to a liquid crystal panel; a drive voltage detecting unit 13 for detecting a drive voltage supplied to the backlight lamp 12 from the inverter 11, and outputting a detected signal DET1 according to the detected drive voltage to a protection circuit unit 15; a drive current detecting unit 14 for detecting a tube current of the backlight lamp 12 and outputting a detected signal DET2 according to the detected tube current to the protection circuit unit 15; and the protection circuit unit 15 for checking a drive state of the backlight lamp 12 based on the detected signals DET1 and DET2, and, if a voltage or a current greater than a predetermined allowable level is detected to be supplied, stopping the drive of the inverter 11 so as to turn off the backlight lamp 12.
A description of an operation of such components will now be given in detail. The inverter 11 is configured to convert the DC voltage inputted from power source into an AC voltage of a level high enough to light the backlight lamp 12, and to output the same to the backlight lamp 12.
The backlight lamp 12 is configured to supply light emitting by being lighted by the boosted AC voltage outputted from the inverter 11, as a backlight, to the liquid crystal panel of the liquid crystal display device. Here, the backlight lamp 12 is implemented as the Cold Cathode Fluorescent Lamp (CCFL) or the External Electrode Fluorescent Lamp (EEFL).
The drive voltage detecting unit 13 is configured to detect a level of the AC voltage supplied to the backlight lamp 12 from the inverter 11, and to output a detected voltage signal DET1 according to the detected level to the protection circuit unit 15.
The drive current detecting unit 14 is configured to detect the tube current of the backlight lamp 12, and to output a detected current signal DET2 according to the detected tube current to the protection circuit unit 15.
The protection circuit unit 15 is configured to check the drive state of the backlight lamp 12 based on the DET1 inputted from the drive voltage detecting unit 13 and the DET2 inputted from the drive current detecting unit 14, and to stop the drive of the inverter 11 if a voltage or a current greater than the predetermined allowable level is determined to be supplied.
The backlight lamp 12 is thusly turned off, thereby preventing the risk of a fire due to a high voltage as well as protecting an operator's safety.
In the backlight drive circuit of the related art liquid crystal display device, the protection circuit unit simply checks the voltage or the current supplied to the backlight lamp, and shuts down the lighting operation of the backlight lamp when it is determined that lighting is impossible due to overvoltage or overcurrent.
However, the protection circuit unit would malfunction if margins for electrically distinguishing a normal lamp from a defective lamp are insufficient, if the condenser of the protection circuit unit undergoes a characteristic change by temperature, or if characteristics of the lamp are changed due to a change in temperature at a periphery of the lamp or surroundings thereof. In this case, the lamp is unnecessarily turned off by the shutdown operation.